When collaborating on a Ruby project, you might run into a situation where you would like to add gems to the project’s gem bundle without adding it to Gemfile, forcing the gems onto your collaborators. Still, you want to have them managed by Bundler.

One such type of gem is an RSpec formatter, like Fuubar. Another example could be the Guard suite of gems.

This is possible to accomplish without any changes to files tracked in the project repository, by leveraging some Git and Bundler configuration directives.

Ignoring our local configuration

First of all, make sure that .bundle/ and Gemfile.local* are ignored by Git. This can be done on a global or on a repository level.

Globally

Set up a global .gitignore file and add the patterns to it.

Run the following commands from anywhere.

git config --global core.excludesfile ~/.gitignore
echo "/.bundle/" >> ~/.gitignore
echo "/Gemfile.local*" >> ~/.gitignore

Per repository

Add the patterns to the non-tracked local exclude file.

Run the following commands from the project repository root.

echo "/.bundle/" >> .git/info/exclude
echo "/Gemfile.local*" >> .git/info/exclude

Setting up our local configuration

1. Create Gemfile.local

   echo 'eval_gemfile "Gemfile"' > Gemfile.local
   echo 'gem "fuubar"' >> Gemfile.local
   echo 'gem "fuubar-cucumber"' >> Gemfile.local
   

2. Create Gemfile.local.lock (assuming the project has a Gemfile.lock file)

   cp Gemfile.lock Gemfile.local.lock
   

3. Tell Bundler to use Gemfile.local

   bundle config --local gemfile Gemfile.local
   

4. Install gems

   bundle install
   

5. Profit!

   bundle exec rspec -f Fuubar
   

Caveats

One caveat with this setup is that Bundler binstubs won’t work unless you set the BUNDLE_GEMFILE environment variable too. This is because Bundler binstubs only read and conditionally set BUNDLE_GEMFILE. They never read .bundle/config.

export BUNDLE_GEMFILE=$(readlink -f Gemfile.local)
bin/rspec -f Fuubar

Another caveat is that updates to Gemfile.lock and Gemfile.local.lock need to be synced manually. If someone else updates Gemfile.lock those changes need to be copied to Gemfile.local.lock. Similarly, if you update a gem, you need to make sure the update is applied to both Gemfile.lock and Gemfile.local.lock.